The encroachment of unwanted plants from forest or swamp on cultivated areas or pasture land has long been a problem. Species such as cedar or juniper shade or cover grass therby reducing the available pasture area. Control by chemical spray is not considered by some environmentalists to be a good solution and frequent mowing and individual extractions by hand when plants are small is too labour intensive. Furthermore some plants have thorns and other characteristics which make such hand labour disagreeable. A further consideration is that merely cutting brush leaves all the roots in the ground to cause other problems including regrowth and difficulties in reseeding.